The present invention relates to an inspection method for inspecting circuit boards (printed circuit board: PCB) by the image processing, in particular, with respect to circuit boards installed in consumers appliances or electronic apparatus such as computers, and relates to the inspection method for inspecting parts in the circuit board and solders connecting those parts,
There are circuit board visual inspection instruments as the inspection apparatus for inspecting the appearance of circuit boards to be installed in electronic apparatus. The circuit board visual inspection instruments are broadly classified into two classes depending upon the image-picture taking method. One is a 2-dimensional imaging apparatus that is a combination of a CCD camera and a lighting apparatus (special lighting apparatus devising light illumination state using such as a ring-shaped light source), and the other is a 3-dimensional imaging apparatus based on the laser trigonometrical survey or the light-section method.
In the conventional circuit board inspection method, in case of implementing the visual inspection of parts installed on an electronic circuit board in accordance with image data obtained by the measurements using the above-mentioned 2-dimensional imaging apparatus or the 3-dimensional imaging apparatus, a region to be inspected, such as a region of interest, ROI, for each part has been set, and then only the ROI for each part has been inspected.
On the other hand, as for an apparatus for inspecting the whole plane of a circuit board, there is an inspection apparatus disclosed in Japanese Unexamined Patent Application Gazette, Hei 4-208803. In this inspection apparatus, from spatial information at three points at which no part is installed on a circuit board, inclination of this circuit board is detected. In this latter conventional inspection apparatus, calculation is made on a plane that was in parallel with respect to the circuit board as the board-approximated plane, and then having this boardapproximated plane as a threshold value, measured image data were converted into binary data; thereby a binary image data was obtained. In this conventional inspection apparatus, based on obtained binary image data, size, position, and inclination of each parts were calculated, and then the results are compared with predetermined standard values, and thereby the installation state of each part on the board were inspected. In such a manner, in accordance with the inspection apparatus disclosed in the Unexamined Patent Application Gazette, Hei 4-208803, it was possible to inspect the whole plane of a circuit board.
In the aforementioned circuit board visual inspection apparatus using one of conventional circuit board inspection methods, inspection regions are previously set up, and inspection was carried out on only those pre-set regions, whereas no inspection was done on other regions than those set regions; as a result, in those cases that electronic parts and solders were placed mistakenly in those regions other than pre-set regions, these were not detected. There was a problem that any inadequate placement of electronic parts and solders could be the cause that would introduce short-circuiting between wirings or abnormal actions, thereby extremely lowering the quality of the circuit board extremely. That is, in those conventional circuit board visual inspection apparatus in which the inspection regions were limited, there was a problem that any cause of the failure as mentioned above, could not be detected.
As the apparatus which solves such the problem in the conventional circuit board visual inspection, there was an inspection apparatus disclosed in the Unexamined Patent Application Gazette, Hei 4-208803, in which the inspection of the parts installation state in the whole area of a circuit board was carried out. In this inspection apparatus, a method was proposed that an approximated plane of a circuit board was calculated as a threshold value from three points at which no part is installed on a circuit board, then condition of the installed part is extracted from this threshold value and the threedimensional information. In accordance with this method, when the heights of the parts that were the objects of the inspection was higher enough than the amount of the deformation of the circuit board, it was possible to extract the electronic parts and solders by the comparison between the three dimensional information of the circuit board and the approximated plane. However, since an actual circuit board has a three-dimensional deformation, in such cases as for miniature-sized parts wherein heights of the inspection objects are lower with respect to the deformation of the circuit board, such the miniaturesized parts are buried by the deformation of the circuit board, it happened that such the miniaturesized parts could not be extracted by the comparison process with respect to the approximated plane. And at those positions where the amount of the deformation of the circuit board is large, it also happened that the circuit board itself was recognized by mistake as the parts of object to be inspected. Particularly, in case of inspecting the miniature-sized parts, which were the trend of recent years, and the printed solder-pastes for connecting those parts, it was not possible to realize a high accuracy extraction of them.
Then, in the present invention proposed here, which proposes a circuit board inspection method which enables to extract, in high accuracy, all the miniature-sized parts placed on a circuit board excluding the influence due to the amount of deformation of the circuit board, it purposes to improve the accuracy of the inspection.
A circuit board inspection method in accordance with the present invention comprises:
(1) a step of measuring the 3-dimensional shape of a circuit board, which is the object of the inspection, thereby setting the data obtained to be surface-shape measured data,
(2) a step of automatically estimating the amount of distortion of the circuit board from the surface-shape measured data of the whole surface of the measured circuit board,
(3) a step of automatically generating an approximated surface shape from the estimated result at the above-mentioned step (2), and
(4) a step of performing a subtraction process between the approximated surface generated at the above-mentioned step (3) and the surface-shape measured data.
The circuit board inspection apparatus is provided with processing apparatus performing the above-mentioned processing steps, thereby extracting in high accuracy those parts other than the circuit board which are placed on the whole surface of the circuit board. Then the circuit board inspection method and the apparatus using this method can carry out the inspection of circuit board in high accuracy by comparing the extracted data with respect to a preset teaching data showing position information and shape information of objects to be inspected in the qualified condition.
The circuit board inspection method in accordance with the present invention comprises:
a measuring process for measuring the surface-shape data of the circuit board on which parts to be measured are placed,
an approximated surface-shape generating process for generating an approximated surface-shape, which is estimating the surface-shape of a circuit board on which objects of interest are not placed, from measured surface-shape data,
a subtraction process for subtracting the approximated surface-shape generated above from the measured surface-shape data,
an ROI (region of interest) determination process for determining those areas which are different from the approximated surface-shape in accordance with the data obtained by the abovementioned subtraction process to be an ROI (region of interest), and
an inspection process for inspecting if electronic parts placed on the above-mentioned circuit board as well as connecting materials for connecting those electronic parts are in a desired state with respect to the determined ROI.
As a result, in the method for inspection of circuit boards in accordance with the present invention, it becomes possible to recognize the objective parts to be inspected placed on a circuit board in high accuracy without being influenced by the distortion of the circuit board by the help of an approximated surface-shape which is approximating the circuit board surface, thereby a high accuracy inspection for the whole surface of the circuit board can be realized.
A circuit board inspection method in another aspect of the invention comprises:
a histogram generating process in which the above-mentioned approximated surface-shape generating process divides measured data of the surface-shape of a circuit board into smaller regions, and generates a histogram in the measured data for the surface-shape in those individual regions,
a circuit board height determination process for determining circuit board heights at predetermined particular coordinate points in respective individual regions from the histogram generated, and
an approximated surface-shape generating process for determining the circuit board height values at other coordinate points than those predetermined coordinate points at which the circuit board height values were already determined by an interpolating process using those already determined height values.
As a result, the method for inspection of circuit boards in accordance with the present invention has a function for generating automatically an approximated surface-shape for the circuit board surface from the surface-shape data of the circuit board on which objects of interest are placed.
In a circuit board inspection method in another aspect of the invention, the above-mentioned histogram generating process comprises:
a process for measuring the amount of reflected light from the circuit board,
an area determination process for determining those areas showing a particular light intensity in measured reflected light amount data, and
a histogram generating process in which, using only those determined areas showing the particular light intensity, a histogram of surfaceshape data for those areas is generated.
As described above, in the method for inspection of circuit boards of the present invention, masking parts of the surface-shape data of the electronic parts, and generating a histogram by using only such data as in areas having higher probability to be the surface of the circuit board itself, thereby the circuit board height is determined with a higher accuracy. And, in the circuit board inspection method of the present invention determines, by masking the parts of interest, the circuit board height can be determined in high accuracy without being dependent on sizes of parts.
In a circuit board inspection method in another aspect of the invention, the above-mentioned histogram generating process comprises:
a process of measuring the color information of the circuit board, and
a process in which, using only such areas showing a particular color information in the above measured color information, a histogram of the surface shape data on that area is generated.
As has been stated above, the circuit board inspection method of the present invention is, utilizing the difference of colors of the surface of the circuit board, and masking the surface-shape data of electronic parts, then by generating the histogram using only those data at a particular portion wherein the probability is high over the electronic circuit, the surface height of the circuit board is determined in higher accuracy. And, in the circuit board inspection method of the present invention determines, by masking the parts of interest, the circuit board height can be determined in high accuracy without being dependent on sizes of parts.
In a circuit board inspection method in another aspect of the invention, the above-mentioned histogram generating process comprises a process in which, using only particular areas in CAD data of the circuit board, a histogram of the surface shape data on that area is generated. As has been stated above, the circuit board inspection method of the present invention is, masking the surface-shape data of electronic parts, then by generating the histogram using only those data at a particular portion wherein the probability is high over the circuit board surface, the surface height of the circuit board is determined in higher accuracy. And, in the circuit board inspection method of the present invention determines, by masking the parts of interest, the circuit board heights can be determined in high accuracy without being dependent on sizes of parts.
In a circuit board inspection method in another aspect of the invention, the above-mentioned area determination process comprises:
a process for generating a histogram in data of the reflection light amount,
a process for determining threshold values by which the histogram regions are divided using the histogram,
a process by which, using the determined threshold values, data of the reflection light amount are area-divided, and
a process for determining those areas having data of a particular light amount.
As a result, areas of particular parts can be extracted from the data of reflection light amount for the circuit board.
In a circuit board inspection method in another aspect of the invention, the above-mentioned board height determination process determines the maximum value of the histogram as the board height value. As a result, the circuit board inspection method of the present invention automatically determines the circuit board height values in divided regions from the histogram of the surface-shape data.
In a circuit board inspection method in another aspect of the invention, an approximated curve of the histogram is obtained, and then the maximum value of the histogram is determined as the board height value. As a result, in the circuit board inspection method of the present invention, the circuit board height can be determined in high accuracy.
In a circuit board inspection method in another aspect of the invention, in the above-mentioned process in which the height of the whole surface is obtained by an interpolation process, the whole surface of the circuit board is approximated to a curved surface by a higher order interpolation process, thereby it is determined as an approximated curved surface. As a result, in the circuit board inspection method of the present invention, the circuit board height can be determined in high accuracy.
In a circuit board inspection in another aspect of the invention, for the above-mentioned approximated curved surface generating process, making a curved surface obtained by adding an offset value to the approximated curved surface generated above to be a new approximated curved surface, and then using this approximated curved surface, the subtraction process is made. As a result, in the circuit board inspection method of the present invention, noise generated under various conditions is suppressed, thereby the recognition accuracy of the parts of interest can be improved.
In a circuit board inspection method in another aspect of the invention, for the abovementioned ROI determination process, the a real values of respective ROI obtained by the above-mentioned subtraction process is calculated, and only those regions that are in a predetermined range are determined as ROI. As a result, the circuit board inspection method of the present invention can eliminate those regions which were recognized faultily by the subtraction process.
In a circuit board inspection method in another aspect of the invention, the above-mentioned ROI determination process comprises reduction and expansion processes, as well as a process of eliminating the minute regions with respect to respective ROI obtained by the above-mentioned subtraction process. As a result, the method for inspection of circuit boards of the present invention determines can eliminate those areas which were recognized faultily by the subtraction process. And, in the circuit board inspection method in another aspect of the invention, in case that the shape of ROI is concave, those regions which could not be recognized in that ROI can be supplemented.
And, in a circuit board inspection method in another aspect of the invention, the above-mentioned ROI determination process comprises:
a process for expanding the ROI,
a process for separating the expanded ROI to a ROI and a board surface region, and
a process for performing the inspection for the separated ROI.
As a result, the circuit board inspection method of the present invention is a process in which, in order to exclude the error in the approximated curved surface, the ROI is extracted once again in minute region in the vicinity of determined ROI, and thereby ROI can be extracted in high accuracy.
In a circuit board inspection method in another aspect of the invention, ROI determined in the above-mentioned ROI determination process are made to be a teaching data which set an inspection reference. As a result, in the circuit board inspection method of the present invention, the setting of the teaching data regions which was set by hands in the conventional method can be made to be an automatic setting process.
And, by combining a plural numbers of circuit board inspection methods, a high-accurate circuit board inspection method can be offered.
A circuit board inspection apparatus in accordance with the present invention comprises:
a measuring section for measuring the data of the surface-shape of the circuit board on which objects of interest are placed,
an approximated surface-shape generating section for generating an approximated surface-shape, which is estimating a surface-shape of a circuit board on which parts of interest are not placed, from measured surface-shape data,
a subtraction section for subtracting the approximated surface-shape generated above from the measured surface-shape data,
an ROI determination section for determining those regions which are different from the approximated surface-shape in accordance with the data obtained by the above-mentioned subtraction process, and
an inspection sections for inspecting if the above-mentioned electronic parts placed on the circuit board as well as connecting materials for connecting those electronic parts are in a desired state with respect to the determined ROI.
As a result, by the circuit boards inspection apparatus in accordance with the present invention, it becomes possible to recognize the parts of interest placed on the circuit board in high accuracy without being influenced by the deformation of the circuit board by the help of an approximated curved surface which is approximating the circuit board surface, thereby a high accuracy inspection for the whole surface of the circuit board can be realized.
While the novel features of the invention are set forth particularly in the appended claims, the invention, both as to organization and content, will be better understood and appreciated along with other objects and features thereof from the following detailed description taken in conjunction with the drawings.